The present invention relates to improved systems and methods for producing and storing pressurized liquefied natural gas (PLNG) and, more particularly, to such systems and methods that synergistically combine the advantages of a natural gas processing plant for producing PLNG, with the advantages of novel containers for storing and transporting PLNG. More specifically, the present invention relates to such improved systems and methods that use a container comprising a load-bearing vessel made from a composite material and a substantially impermeable, non-load-bearing liner in contact with the vessel.
Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
U.S. patent application Ser. No. 09/099,268 (the xe2x80x9cPLNG Patent Applicationxe2x80x9d), having International Patent Application Number PCT/US98/12726 and International Publication Number WO 98/59085, and entitled xe2x80x9cImproved System for Processing, Storing, and Transporting Liquefied Natural Gasxe2x80x9d, describes containers and transportation vessels for storage and marine transportation of pressurized liquefied natural gas (PLNG) at a pressure in the broad range of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature in the broad range of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.). Containers described in the PLNG Patent Application are constructed from ultra-high strength, low alloy steels containing less than 9 wt % nickel and having tensile strengths greater than 830 MPa (120 ksi) and DBTTs (a measure of toughness, as defined in the Glossary) lower than about xe2x88x9273xc2x0 C. (xe2x88x92100xc2x0 F.). As discussed in the PLNG Patent Application, at the preferred operating pressures and temperatures of the invention described therein, about 3xc2xd wt % nickel steel can be used in the coldest operating areas of a PLNG plant for the process piping and facilities, whereas more expensive 9 wt % nickel steel or aluminum is generally required for the same equipment in a conventional LNG plant (i.e., a plant for producing LNG at atmospheric pressure and about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.)). Preferably, high strength, low alloy steels with adequate strength and fracture toughness at the operating conditions of the PLNG plant, are used to construct the piping and associated components (e.g., flanges, valves, and fittings), pressure vessels, and other equipment of the PLNG plant in order to provide economic advantage over a conventional LNG plant. U.S. patent application Ser. No. 09/099,569 (the xe2x80x9cProcess Component Patent Applicationxe2x80x9d), having International Patent Application Number PCT/US98/12725 and International Publication Number WO 99/32837, and entitled xe2x80x9cProcess Components, Containers, and Pipes Suitable For Containing and Transporting Cryogenic Temperature Fluidsxe2x80x9d, describes process components, containers, and pipes suitable for containing and transporting cryogenic temperature fluids. More particularly, the Process Component Patent Application describes process components, containers, and pipes that are constructed from ultra-high strength, low alloy steels containing less than 9 wt % nickel and having tensile strengths greater than 830 MPa (120 ksi) and DBTTs lower than about xe2x88x9273xc2x0 C. (xe2x88x92100xc2x0 F.). The PLNG Patent Application and the Process Component Patent Application are hereby incorporated herein by reference.
The PLNG Patent Application and the Process Component Patent Application utilize ultra-high strength, low alloy steels as the connecting theme between the PLNG plant and the containers used for storing and transporting the PLNG. If use of the steels for constructing the containers did not provide a commercially viable means for storing and transporting the PLNG on marine vessels, then any use of the steels in the plant would be meaningless since there would be no mechanism for commercially transporting the PLNG produced by the plant. Conversely, while use of the steels in the PLNG plant generates some economic savings over conventional LNG operations, the most substantial economic benefit is derived from the enormous simplification (and consequent cost reductions) in the plant. Because of its relatively simple design, the PLNG plant is substantially cheaper than a conventional LNG plant of similar capacity. Additionally, while use of the steels in the PLNG transportation system is commercially viable and does generate some economic savings over conventional LNG operations, the weight of the steel containers is high compared to that of its PLNG cargo, resulting in a relatively low cargo-carrying capacity performance factor (PF). The PF for compressed fluid storage containers relates the pressure exerted by the cargo (P) to the volume (V) of the container and the weight (W) of the container by the equation PF=PV/W. What is currently missing from the all-steel PLNG system (i.e., plant plus transportation) is a combination of the PLNG plant with a low cost, higher PF, container-based transportation system that is capable of handling PLNG.
U.S. Pat. No. 3,830,180 (xe2x80x9cBoltonxe2x80x9d) discusses use of a double-walled, composite cylindrical vessel configuration for transport of regular LNG, i.e., LNG at atmospheric pressure and at temperatures of about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.). The cylindrical vessel configuration is preferred because it maximizes use of the space available in a transportation vessel. However, the load-bearing, inner wall of Bolton""s vessel is designed for a maximum pressure of approximately 50 to 60 pounds (psi) and, thus, Bolton""s vessel is not suitable for transport and storage of PLNG. Additionally, although Bolton""s cylindrical vessel configuration may appear, theoretically, to improve the cargo-carrying capacity performance factor (PF) for transport of a given fluid over that of the steel containers described in the PLNG Patent Application, Bolton""s design has several economic and technical limitations on size, fabrication methodology, and reliability. The use of a weldable homogeneous material for partial load bearing reduces the potential weight savings associated with a composite vessel design. Moreover the double-walled concept unduly increases the effective wall thickness, complicates the overall fabrication methodology, decreases the technical and economic feasibility of the design, and results in poor utilization of the space available on a ship for transporting cargo. Further, the design by Bolton requires the use of a homogeneous material that can be welded to form the load-bearing, inner vessel wall, which consists of two domes welded to a cylindrical mid-section. The stress concentration associated with the two welds warrants protection of the welds by using a complicated pre-stressed stay-tube arrangement. Finally, the welds in Bolton""s vessels are potential sources of pitting and, consequently, of premature failure.
Both U.S. Pat. No. 5,577,630 (Blair et al.) and U.S. Pat. No. 5,798,156 (Mitlitsky et al.) describe lined, composite pressure vessels for storing and transporting compressed natural gas. Blair et al. discusses pressure vessels manufactured by overwrapping a liner with a composite layer using filament winding, tube rolling, tape wrapping, automated fiber placement, or another method familiar to those of skill in the art, to obtain a vessel configuration which approximates a rectangular volume for use in compressed natural gas (xe2x80x9cCNGxe2x80x9d) vehicles. U.S. Pat. No. 5,499,739 (Greist, III et al.) discusses a thermoplastic liner made of a modified nylon 6 or nylon 11 material for use in a pressure vessel to control gas permeation and allow operation at low temperatures, the low end of which is stated to be xe2x88x9240xc2x0 F. The vessels of Greist, III et al. are made by a method of overwrapping filaments in a predetermined pattern around the thermoplastic liner for improved mechanical properties and processing. U.S. Pat. No. 5,658,013 (Bees et al.) discusses a fuel tank for vehicles for holding and dispensing both a liquid and gaseous fuel, and suggests that fully-composite or fiberglass reinforced materials could be used in construction thereof. The liquid fuels discussed in the patent are conventional liquid fuels at ambient temperature and pressure. Both Bees et al. and Mitlitsky et al., previously discussed, propose precious metal-coated, polymer-based liners that provide further enhancements in performance factors of their tanks/vessels. However, the complexity and hence high cost of the metal deposition process and the liner fabrication process make the tanks/vessels of Bees et al. and Mitlitsky et al. suitable primarily for applications where maximized payload-carrying capacity is the primary objective and, thus, low tank/vessel weight is of very high premium. U.S. Pat. No. 5,695,839 (Yamada et al.) discusses a composite container which is required to have a gas barrier property, wherein the packaging material for constituting such a container is caused to have a laminate structure, and a layer of an aluminum foil is disposed or interposed in the laminate structure. However, none of the containers discussed in these publications are designed for containing fluids that are at both cryogenic temperatures (less than xe2x88x9240xc2x0 C. (xe2x88x9240xc2x0 F.)) and high pressures, such as the temperatures and pressures of PLNG.
S. G. Ladkany, in xe2x80x9cComposite Aluminum-Fiberglass Epoxy Pressure Vessels for Transportation of LNG at Intermediate Temperaturexe2x80x9d, published in Advances in Cryogenic Engineering, Materials, volume 28 (Proceedings of the 4th International Cryogenic Materials Conference), San Diego, Calif., USA, Aug. 10, 1981-Aug. 14, 1981, discusses the design of pressure vessels for the transportation of liquefied natural gas (LNG) at temperature and pressure conditions between the critical conditions, 191 K, 4.69 MPa (xe2x88x92116xc2x0 F., 680 psi) and atmospheric conditions 106 K, 0.1 MPa (xe2x88x92268xc2x0 F., 14.7 psi). Ladkany discusses in his paper that a liquid nitrogen containing, aluminum-composite vessel, of the type with a thin metal liner totally surrounded by and bonded to the overwrap covering it, was successfully tested at the Beech Aircraft Corporation. However, Ladkany opts for a large (6 m (20 ft)) diameter cylindrical, 47 mm (1.85 in) thick, welded aluminum pressure vessel for containing the intermediate temperature LNG. Ladkany""s aluminum vessel is circumferentially reinforced with 17 mm (0.67 in) thick layers of high strength fiberglass epoxy or 51 mm (2 in) thick layers of pultruded glass polyester overwrap and stiffened against buckling by circumferential frames that are placed at 2.16 m (7.1 ft) intervals. The stiffening frames are also used for structurally supporting and fastening the free-standing vessel during transportation and operation.
In spite of the aforementioned advances in technology, systems and methods for producing and storing pressurized liquefied natural gas (PLNG) that synergistically combine the benefits of the PLNG processing plant, for producing PLNG, with low cost containers having a substantially improved PF, for storing and transporting PLNG, do not currently exist. It would be advantageous to have such systems and methods.
Therefore, an object of this invention is to provide such systems and methods. Other objects of this invention will be made apparent by the following description of the invention.
Consistent with the above-stated objects of the present invention, systems and methods for producing and storing pressurized liquefied natural gas (PLNG) are provided, wherein the systems and methods include (a) a natural gas processing plant suitable for producing pressurized liquefied natural gas at a pressure of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.); and (b) at least one container suitable for storing the pressurized liquefied natural gas, the at least one container comprising (i) a load-bearing vessel made from a composite material and (ii) a substantially non-load-bearing liner in contact with the vessel, said liner providing a substantially impermeable barrier to the pressurized liquefied natural gas. The load-bearing vessel is suitable for withstanding pressures of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and temperatures of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.).